In various applications, heating elements such as positive-temperature-coefficient (PTC) heating elements or resistive wire heating elements are employed. E.g., in automotive applications heating elements are used to provide fast and convenient heating of a vehicle interior.
Typically, a plurality of PTC heating elements are controlled independently by respective mechanical relays. E.g., if a higher (lower) heating power is required, a larger (smaller) number of mechanical relays are operated in a closed position to provide supply currents to the respective heating elements. Here, a granularity of adjustment of the total heating power is typically comparably low; i.e., a number of heating levels which may be implemented may be small. If, e.g., three PTC heating elements are employed either in on or off state, then four heating levels are available.
Sometimes, it may be required to provide a finer granularity of adjustment of the total heating power; i.e., sometimes it may be desirable to increase the number of heating levels.